HR: 0830h
AN: H21B-05    [Abstracts]
TI: Salinization of Surface Water and Groundwater, Hueco Bolson and Mesilla Valley, New Mexico, Texas and Chihuahua: Sources of Sulfate as Indicated by Stable O, H and S Isotopes.
AU: * Eastoe, C J
EM: eastoe@geo.arizona.edu
AF: SAHRA, Department of Geosciences, University of Arizona, Tucson, AZ 85721 United States
AU: Dadakis, J S
EM:
AF: Orange County Water District, PO Box 8300, Fountain Valley, CA 92708 United States
AU: Hibbs, B J
EM:
AF: CEA-CREST, Dept of Geological Sciences, California State University-Los Angeles, Los Angeles, CA 90032 United States
AU: Hogan, J F
EM:
AF: SAHRA, Dept. of Hydrology and Water Resources, University of Arizona, Tucson, AZ 85721 United States
AU: Granados Olivas, A
EM:
AF: Geographic Information Center, Universidad Aut¢noma de Cd. Ju rez, Av. Del Charro 610 norte, Cd. Juarez, Chi 32310 Mexico
AU: Druhan, J
EM:
AF: SAHRA, Dept. of Hydrology and Water Resources, University of Arizona, Tucson, AZ 85721 United States
AB: Salinity and δ³⁴S values in Rio Grande surface water increase downstream within the Hueco Bolson, with sharp increases detected in El Paso and near Fabens at times of low flow. Fluctuations at El Paso reflect variations in relative input of high-δ³⁴S salty groundwater discharging from the Mesilla Valley upstream. Near Fabens, further addition of water with δ³⁴S > 9 ‰, [SO4] > 300 mg/L and Cl/SO4 near 1 is required. Such water can be derived from Hueco Bolson groundwater north of the river or from salty sediment beneath the flood plain, but not from urban effluent or agricultural drainage. Sulfate δ³⁴S and δ¹⁸O values are consistent with Hueco Bolson groundwater as the source of high-δ³⁴S sulfate. The origin of flood-plain groundwater is identified as pre-dam (pre-1916) or post-dam river water according to degree of evaporation as expressed in O and H isotope content. Sulfate geochemistry and salinization mechanisms differ in the two types of groundwater. Pre-dam groundwater in Hueco Bolson and Mesilla Valley has increased in salinity relative to contemporaneous river water as a result of addition of salty basin water with δ³⁴S > 9 ‰; and Cl/SO4 > 1 in the Hueco Bolson where interaction with salty sediment below the flood plain is likely. Post -dam groundwater salinity in the Hueco Bolson has increased by addition of sulfate with δ³⁴S commonly lower than values in present-day river water, and can be explained by oxidation of sulfide in alluvium, but not by addition of urban wastewater, or of gypsum and sulfuric acid as agricultural amendments. Post-dam groundwater salinity in the Mesilla Valley most commonly results from addition of salty basin water with δ³⁴S > 8 ‰, [SO4] > 200 mg/L and Cl/SO4 >2.
DE: 1040 Isotopic composition/chemistry
DE: 1806 Chemistry of fresh water
DE: 1829 Groundwater hydrology
DE: 1831 Groundwater quality
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: 2005 Joint Assembly